The present invention relates to equipment for use at life-saving/heart and lung resuscitation (so called CPR), and in particular a device for placing on the chest of a patient to cooperate with the hands of a person who performs chest compressions. The device is, in particular, arranged to emit a sound when the chest compression is performed with a force that exceeds a predetermined value. Even more specifically, the device is defined by the features that are given in the ingress of the subsequent claim 1.

Several studies have shown poor skills within learning and remembering heart and lung resuscitation (CPR). This has been thoroughly discussed by Kaye and Mancini (Kaye W, Mancini ME. Teaching adult resuscitation in the United States - Time for a rethink, Resuscitation 1998; 37:177-87).

During testing with dolls, there are few compressions and ventilations that are carried out correctly, where a rhythm which is too slow, insufficient depth of compression, and insufficient blowing in, are the most common mistakes. Similarly, one found at a study of CPR quality that, with regard to the patient, fewer than half of the passers-by carried out a good CPR, defined as a significant pulse during chest compressions and chest expansions. Even if expansion of the chest can be observed by another person, there are few unskilled persons (and also medical personnel) who can palpate a pulse accurately. Consequently, unskilled persons are no longer trained to, or expected to be able to, carry out a pulse control. (Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Supplement to Circulation 2000; 102; 122-59).

Consequently, there was a need for an alternative method to ensure sufficient chest compression where this shall easily be able to be used by unskilled persons. One reason that rescue personnel do not compress the chest hard enough is, to a large extent, because they are afraid of injuring the patient by either pressing too hard or pressing at the wrong place. A simple device that makes it easier to press at the right place and

warns the rescuing person when the compression is strong enough ought to contribute to alleviating this concern.

Good chest compressions are defined (according to the Guidelines 2000 given above) as those that compress the chest of a grown person 4 cm with a frequency of 100 per minute. To force the chest of a grown person that far down requires a force of about 35 kp. For a child, the chest ought to be compressed about 2.3 cm, which requires a force of about 20 kp. Audio messages have been found to improve the compression and ventilation rhythm and are recommended to be used in CPR (Guidelines 2000).

Devices that encompass a pressure gauge have been available for many years. When these are placed on the chest of a patient, they will guide the rescue personnel with regard to how much force to use. Lately, a device has come on the market that combines this function with audio messages to control the timing of the chest compressions. (Boyle AJ et al. Improvement in timing and efficiency of external cardiac compressions with a new non-invasive device: The CPR Ezy. Resuscitation 2002; 54: 63-7).

In general, CPR-Ezy is a rectangular device that is placed between the hands of the rescuer and the chest of the patient. It encompasses a LED screen that gives visual information about the force used. The device also incorporates an electronic metronome that gives out both sound and light.

CPR-Ezy and similar devices are too expensive (USD 150 to USD 250) and elaborate to be used to any large extent by unskilled persons. In comparison, ventilation aids are, to a large extent, used by unskilled persons; they normally cost around USD 2 to USD 15 and fit into a wallet or a pocket. Furthermore, CPR-Ezy is dependent on an electrical power source, for example a battery. A battery can be subjected to losing power even when not in use. An unskilled person can carry this around for many years before a situation arises where it can be necessary to use it. At this time the battery may be flat and the device will be useless. If there is still life in the battery, the rescuer must give all his visual attention to the LED screen to see if the compression is good enough. This means that he is not able to observe the reactions of the patient while carrying out the

compressions. A LED screen is also difficult to see in strong light, for example, in sunlight. Furthermore, the rescuer will normally have to make contact with emergency services via a telephone. There the health personnel can give him instructions. If the health personnel can hear over the telephone how the rescuer performs the compressions with sufficient force or not, it is easier for them to provide assistance. In CPR-Ezy, the lack of sound that indicates compression force will prevent the health personnel from getting this valuable information.

Another previously known device is shown in US Patent 4,554,910. This device has an underside which is intended to be placed on the patient's chest and an upper side which the rescuer presses against. A spring and a rectangular spring body in steel are between the surfaces. The steel spring body has sidewalls with inwardly directed recesses. When the steel spring body is forced together, the recesses will bend outwards and emit an audible click.

Even if this device gives an indication of when the required pressure has been achieved, and is not dependent on batteries, it is of a size that makes it impractical to be carried around and it does not fit into most pockets. This implies that the device is of limited availability.

US 4,863,385 is a completely electronic device. It appears to look very advanced, as it comprises a synthetic voice, indicator lamps and buzzers. It can also be set for people of different sizes and it can detect a pulse. However, it does not comprise any detection of the force that is used for the chest compression. Therefore, apart from the pulse measurements, this known device is nothing but an instruction book. The aim is that the user shall turn on the device, and the device shall thereafter provide instructions to the user (in the form of a synthetic voice) about what he shall do, and also the order and timing of the actions. The device has an outer manual switch that can be turned from off to one of four different on-positions.

Thus, the device has, according to this publication, no possibility to detect that the user is carrying out chest compression with sufficient force.

US 5,496,257 also shows a completely electronic device, which shows the force of the chest compression in a display 50. It is also mentioned that audible signals can be emitted if the force of compression is too large or too small.

In this device there is also an external switch that can be operated from an off position to one of two on-positions. Each of the on-positions is connected to a separate battery, so that the user shall have an extra power source if one of the batteries is flat. However, the device is completely dependent on electrical power. If both batteries are flat, the device will be of no use.

US 6,013,041 shows a device that is meant for, and only applicable to, simulation of chest compressions. Therefore, it is formed as a long telescopic tube that gives a certain compression travel. This shall give an approximately, realistic movement during the training. The device is not suitable for use on a patient. If one tries this, the device would take up much of the movement and the force from the operator. One would thereby not have any control over how much movement and force that is transferred to the patient, as little as if one put several cushions or mattresses between the hands of the operator and the patient. Furthermore, due to its length, the device would be very difficult to control, as it could easily flip sideways during the compression.

On the basis of the above, Laerdal Medical AS developed an aid to improve the timing and efficiency of chest compressions, both during training and at use on a patient, at a price and a size that makes it possible for all unskilled persons to buy it and carry it around at all times.

The result was a device for placing between the hands of a person who performs chest compressions, and the chest of a patient, comprising a first part and a second part, where the first part and the second part can be moved against each other when compression is carried out. There is a return device between the first and the second part to move the parts away from each other again when the compression is released. In the simplest embodiment form, the device has a mechanical sound generator to provide a

sound when the parts are moved against each other with a force that exceeds a predetermined value. The mechanical sound generator comprises a plate suspended in one end, where the opposite end of the plate is free, and where the plate is formed such that it provides a sound when a force that exceeds a predetermined value is exerted against the free end of the plate.

This device is described in detail in WO 2004/056303, which is hereby incorporated in the present application by reference,

Even if this chest compression device functions very well, one has, over some time, found that improvement potential exists. The lifetime of the plate has been found to be shorter than one could wish for. The chest compression device has been found to be used successfully by ambulance personnel. Recent investigations reveal that even trained resuscitators make mistakes, which can be of importance for the success of the resuscitation attempts. If such a chest compression device shall have a wider application among trained personnel, who will use the chest compression device both more frequently and over a longer time than unskilled persons, the lifetime of the plate should be increased.

It has been found that the lifetime of the plate can be drastically increased in that the plate is prestressed when fitted in the chest compression device. The reason for this is possibly that the plate must then be subjected to considerably smaller movement before it is turned inside out and one hears a click. According to the invention this is achieved in that the plate is fixed and prestressed to a certain curvature that does not exceed the curvature at which the plate suddenly changes its bending stiffness.

The plate is preferably, at its one end, held fast in a fixture and, at its other end, led under one or more barbs that hold the plate in a curved state. This leads to a simple and sure fixing, and that the plate is easy to fit.

The plate is preferably, over a part of its length from the end edge that is fitted to the fixture, supported by at least one arched contact face. This leads to an even curvature of the plate so that the tension is distributed across the plate surface. In an alternative embodiment form, the plate is supported at about the middle of its longitudinal axis with the help of a middle support and is prestressed in that it is held at each end in a curved state with the help of prestressing holders. This implies that the plate can be larger and one thereby gets the tension more evenly distributed.

The prestressing holders preferably encompass barbs under which the plate is led. This ensures that the plate is simpler to fit and that it can move freely in the subsequent curvature.

The invention shall now be explained in more detail with reference to the embodiment examples that are shown in the enclosed figures where:

Figure Ia shows a section in perspective of one half of a chest compression device in a first embodiment form of the invention with a fixture for fastening of a click metal plate,

Figure Ib shows, corresponding to figure Ia, where a click metal plate that is not prestressed is inserted,

Figure Ic shows, corresponding to figure Ib ₅ but with a prestressed click metal plate,

Figure 2 shows a section through the click metal plate and the holder for this in figure Ib and

Figure 3 shows a perspective diagram of the one half of a chest compression device in a second embodiment form of the invention.

The first embodiment form that is shown in the figures Ia, Ib, Ic and 2 shall be initially referred to.

Figure Ia shows in perspective a section of a lower half 1 of a chest compression device according to the invention. A fixture 3 that is comprised of a gable 5 and side members 6 is integrated in the lower half. Furthermore, prestressing holders 9 are arranged at some distance from the fixture 3. A projection 8 protrudes from about the middle of the gable 5. The projection 8 has a peg 12 at its outer end, which is arranged to be led into a hole (not shown) in a plate 2 (see figure Ib). The side members 6 are fitted with curved contact faces 7. The prestressing holders 9 stand in the extension of the side members 6, but at a distance from these. The prestressing holders 9 comprise a trunk 11 that is fitted with barbs 10. The distance between the prestressing holders is adapted to the width of the plate 2, so that the distance between the trunks 11 is somewhat larger than the width of the plate, while the distance between the barbs 10 is somewhat smaller than the width ofthe plate 2.

When the plate 2 (see figure Ib) is put in place, it is led in underneath the projection 8 and is placed down against the curved contact faces 7. The plate 2 is thereby not lying prestressed as shown in figure Ib.

When the plate is brought into this position, the free end of the plate 2 is forced down and beyond the barbs 10 on the prestressing holders 9. As the distance between the barbs 10 is smaller that the width of the plate 2, the plate 2 will be lying on the underside of the barbs 10. The height of the barbs 10 is adjusted so that the plate 2 is bent when it engages with the barbs 10. The curvature can be so large that it is just before the plate 2 "clicks", i.e. that the bending stiffness changes abruptly. Plates that are formed so that the bending stiffness changes abruptly when bending above a certain angle are well known to a person skilled in the arts and are also explained in WO 2004/056303. Therefore, how such a plate is constructed will not be explained in more detail.

Viewed in a section according to figure 2, one can see that the click metal plate 2 with its one end is inserted into the fixture 3 at the gable 5.

The plate 2 lies in an arch over the curved contact faces 7 and stretches further in an arch to the underside of the barbs 10. The curvature of the contact faces 7 and the placing of the barbs 10 are adjusted so that the plate arches evenly when in a prestressed state.

When the chest compression device is used, a pressure device (not shown) that can be a screw or a peg at the upper half of the chest compression device, will be forced against the plate 2 in an area at the outer free end of the plate. The plate 2 will then be further curved and, at a certain pressure force, it will suddenly change bending stiffness and emit an audible clicking sound.

When the plate 2 goes through a bending movement, this will result in wear on the plate 2. When being bent repeatedly in quick succession, the bending movement will lead to the plate being heated up. The heating up will, over time, lead to development of a breakage. This is the same mechanism that is in operation when one wants to break a steel wire. One bends it several times in quick succession and will eventually get a small weakening of the material, which develops into a rupture across the wire.

As the plate 2, according to the present invention, is already curved a part of the curvature it must go through before it clicks, the bending movement of the plate 2 will become relatively small. When the plate is strained several times at the pressure device, the total travel of the plate 2 will be considerably reduced. The heating up will thereby be reduced and the lifetime of the plate will increase. At the fixing, according to the embodiment form in the figures Ia, Ib, Ic and 2, it is ensured that the plate is bent as evenly as possible. Tension concentrations are thereby avoided and the lifetime is further increased.

Figure 3 shows an alternative embodiment form of the invention. Here, a middle support 15 is arranged on the lower half 1. The plate 2 is placed over the middle support 15 and is bent down underneath the barbs 10 on the prestressing holders 9. There are in all, four prestressing holders 9 here, that are arranged so that they grip the plate 2 on opposite end edges on each side of the middle support 15 in pairs.

In this embodiment form, a dome 16 is also drawn in the middle of the plate 2. This dome 16 goes down toward the support 15 when the plate is not bent above a certain curvature. Therefore, the support 15 has a protrusion 17 below the dome 16.

During chest compression, a pressure device 18 will force against the plate near each end of the plate at the barbs 10. Thus, the plate will be strained at each end. This leads to a more even distribution of the curvature over the length of the plate than the embodiment form according to the figures Ia, Ib, Ic and 2. At a certain curvature, the dome 16 will be changed from curving downwards to the support 15 to curving upwards from the support 15. At the moment this occurs, the plate will emit a click.

The embodiment form according to figure 3 offers a possibility for a plate that is even larger than the embodiment form according to the figures Ia, Ib, Ic and 2. The tension in the plate is thereby distributed over an even larger surface.

The placing of the barbs is not critical and neither is the number. However, the placing and the number can be significant for how even the curvature will be on the plate and thereby will also be important for the distribution of the tensions.

In an alternative embodiment, one can use the pressure mechanism (represented by the pressure devices 18 in figure 3) to prestress the plate. This can be carried out by using a screw as a pressure device and screw this so far down that it touches the plate and bends this to a desired prestressed state. The travel that is required to bend the plate until it clicks will thereby be reduced.